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Brainstem discovered as important relay site after stroke

After a stroke, sufferers are often faced with the problem of severe movement impairment. Researchers at the Brain Research Institute of the University of Zurich have now discovered that the brainstem could play a major role in the recovery of motor functions. The projection of neurons from this ancient part of the brain into the spinal cord leads to the neural impulses needed for motion being rerouted.

Around 16,000
people in Switzerland suffer a stroke every year. Often the result of a sudden occlusion
of a vessel supplying the brain, it is the most frequent live-threatening
neurological disorder. In most cases, it has far-reaching consequences for
survivors. Often the stroke sufferers have to cope with handicaps and
rehabilitation is a long process. The brain does, however, have a “considerable
capacity for regeneration” explains Lukas Bachmann from the Brain Research
Institute of the University of Zurich. As member of Professor Martin Schwab’s
research team, he found that the brainstem, the oldest region in the brain,
could play an important role in recovery. The results have now been published
in “The Journal of Neuroscience”.

The healthy half of the brain assumes control

A stroke in
the cerebral cortex frequently leads to motor constraints of one half of the
body, to what is known as hemiparesis. This is due to the loss of neuron
pathways which transmit signals from the cortex to the spinal cord. As these
pathways are crossed, the side of the body contralateral to the affected half
of the brain is affected. The major impairments at the beginning are often only
temporary and stroke sufferers can sometimes stage an amazing recovery. “The side
of the body affected is increasingly controlled by the ipsilateral side of the cortex,
i.e. the healthy side”, explains Lukas Bachmann. As the neuron pathways are crossed,
this raised the following question for the neuroscientists: by which pathway are
the signals rerouted from the motor cortex to the ipsilateral parts of the spinal
cord?

Sprouting of neurons from the brainstem

In their
study in mice the researchers in Martin Schwab’s team now demonstrate that the
brainstem probably plays a key role in the rerouting of neural impulses. Images
of the brain show that after a major stroke nerve fibers from specific core regions
of the brain sprout into the area of the spinal cord that had lost its input after
a stroke. “At the same time, more fibers sprout from the intact cortex into
these same regions of the brainstem”, continues Lukas Bachmann. These changes
in the neuronal circuits may mediate the non-crossed flow of nerve impulses after
a stroke. “This could turn out to be a key mechanism which facilitates recovery
after a stroke”, says the brain researcher. The scientists now want to use
these findings to steer the sprouting of neurons in various areas of the brain
by means of targeted therapy to maximise the recovery of motor functions.